Study of the precipitation of fission products and corrosion products under the radiolytic effects of solvents for reprocessing

In the Purex process, extraction disturbances are, sometimes caused by the formation, at the aqueous/organic interface, of emulsions stabilized by solids called 'crud'. In relation with this phenomenon, we investigate under accelerated conditions the precipitation of fission or corrosion products in a 3M nitric acid/TBP 30 %-dodecane system, using electron irradiations. It is shown that only iron and palladium markedly precipitate. Iron behavior is related to Fe(DBP)3 formation, which precipitates for too high HDBP concentrations (3g.l-1) by comparison with process values. Palladium precipitation is related to dodecane degradation and needs high irradiations (0.20 MGy). Zirconium precipitation is not noticed until 0.25 MGy, irradiations leading only to its extraction in the organic phase. Thus, zirconium precipitation with TBP degradation products has been studied. With HDBP, precipitation is limited and occurs for 1,5 < HDBP/Zr < 6. With H2MBP, precipitation is marked, without dissolution by excess of H2MBP. So, it is suggested that zirconium precipitation in the process occurs in the organic phase, after extraction of this element by degradation products, this phenomenon occuring in areas of the extractors where solvent is not well mixed. Moreover, it is shown that all these precipitates, which simply form a deposit at the interface, are mainly not effective in stabilizing emulsions and cannot be the simple (or single) cause of 'crud'. (author)